Air pointers may be used as a remote control in many different situations and may have diverse functions. For example, a remote control of an audiovisual apparatus (television, reader/recorder of disks, hi-fi system) can be used to select a program or choose a function from a menu. A remote control of a household apparatus may be used to point at the apparatus to command the execution of a specific function. When an air pointer is used as a computer remote control, the pointer can be programmed as a function of the applications executed by the computer. In an electronic game interface, depending on the game, the pointer may emulate an object manipulated by the user (golf club, tennis racket, bowling ball, handgun, etc.). An air pointer may also provide an assistance for the man-machine interface or serve as a remote control intended for persons with reduced mobility: for example, an air pointer can be fixed to the head, the spectacles, an earpiece, or any other part tied to the movements of the head, so as to aid persons with motion deficiency or who are unable to use a conventional hand-held mouse. In general, the air pointer is equipped with buttons which allow selection of a command, or which can be programmed to execute a function (or a service). The buttons can also be used to associate different pointer states during pointing gestures by recognizing the gestures from some characterizing features and/or a matching with a database of specific gestures.
The movements of the pointer in space comprise rotations and translations. They can be measured by sensors of various types. For example, cameras or image sensors can measure rotations and translations simultaneously by comparison of successive images and using geometric transformations. Alternatively, a combination of magnetometers, accelerometers and/or of gyrometers can measure translations and rotations about several axes of the air pointer. A system comprising a combination of one or more cameras and several magnetometric, accelerometric and/or gyrometric sensors can be used to improve measurement accuracy and redundancy.
The general problem that these applications of motion sensing pointers must solve is to take account of the manner in which the user holds the pointer, in particular the orientation of the pointer in space. If the pointer has rotated in the hand of the user along its longitudinal axis and is held for example at 45°, a horizontal or vertical motion of the pointer will result in a diagonal motion on the screen to which the pointer is pointing. This phenomenon is known by the name “tilt” or torsion. It should therefore be corrected in order for the pointer to be more user friendly.
A first option for solving this problem is to provide mechanical means so that the sensors remain in a substantially fixed position in the frame of reference of the screen when the user imparts a torsion motion to the pointer. It is thus possible to provide for the sensor or sensors to be mobile within the pointer in the manner of a pendulum whose base has sufficient inertia to remain substantially fixed in spite of the torsion movements imparted to the pointer. Such a device is disclosed by U.S. Pat. No. 5,453,758. It is also possible to encapsulate said sensors in a stabilization device consisting of a pair of spheres tied to the pointer by rotation axes, as is the case in a compass aboard a boat or an aircraft. Such a device is disclosed by U.S. Pat. No. 5,440,326. A first drawback of these mechanical devices for compensating for the torsion of the pointer is that they are limited to restricted spans of angles of torsion and rates of displacement. A second drawback is that these devices are bulky. A third drawback resides in the mechanical inertia of these devices and the delay in the horizontal alignment induced, thus barring them from real-time pointing applications.
A second option for compensating for the torsion of the pointer consists in computing the angles of torsion by using the measurements of some of the sensors embedded aboard the pointer, notably accelerometers. The computed angles of torsions are then used to perform a transformation of the measurements of the sensors from the reference frame of the pointer into the reference frame of the screen by applying to said measurements one or more rotation matrices whose coefficients are dependent on the calculated torsion angles. Such procedures are disclosed notably by i) patent U.S. Pat. No. 5,902,968 where the main sensor is a gyrometer and the sensor for computing the angle of torsion is an accelerometer, ii) patent application US 2004/0075650 where the main sensor is a camera coupled to accelerometers, the combination allowing tilt correction, iii) patent application US 200210140745 where the main sensor is a GPS receiver and the tilt correction sensor a set of accelerometers and iv) patent U.S. Pat. No. 7,158,118 where the main sensor consists of one or more gyrometers and the tilt correction sensor consists of one or more accelerometers. These procedures have the drawback of providing noisy and inaccurate results insofar as the torsion angles are computed by using trigonometric calculations which are not adapted to fixed point/small memory processors which are preferably used in low cost air pointing devices.
A new way of correcting the tilt has been disclosed by U.S. Pat. No. 8,010,313 assigned to the assignee of the present application. According to this invention, instead of computing the tilt angle with the canonic trigonometric formulas, the measurements of the accelerometers are directly used to correct the measurements of the gyro sensors.
It has also been found that it may be advantageous to use only one accelerometer measurement at a moment in time to accomplish the tilt correction, so as to simplify the calculation of the correction and use less computing power, which is then freed for other tasks. Also, when an accelerometer axis is close to the vertical, the variation of the accelerometer signal due to a change in the roll angle is small compared to the noise level. Therefore, the values close to 1 lack precision and the roll correction along this axis is not accurate for angles higher than around 70°, leading to an overall bias affecting the cursor movements on the display. PCT application filed as PCT/EP2011/056925 assigned to the applicant of the current application proposes a solution to this class of problems.
None of these prior art references, though, discloses solutions which are well suited to use cases where the user imparts significant dynamics to the pointer. In these use cases, the measurements of the accelerometers comprise a proper acceleration component which cannot be neglected. Therefore, since what is needed is the gravity component of the accelerometers measurements, the proper acceleration components create deviations of the cursor to be controlled from the trajectory it should follow to properly convert the movements intended by the user. Low pass filtering the outputs of the accelerometer, as proposed by U.S. Pat. No. 7,158,118 does not provide a solution to this problem since low pass filtering only averages the proper acceleration components, but does not eliminate them. Moreover, using a low pass filter makes the system less responsive.